Coulomb’s law

Coulomb’s law, or Coulomb’s inverse-square law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles; or the force exerted by an electric field on an electric charge. In physics, the Coulomb force, described by Coulomb’s law, is the force exerted by an electric field on an electric charge. It is the force acting between electrically charged objects, and it is operationally defined by the value of the interaction between two point-like and stationary electric charges in vacuum.

From Coulomb’s law we can see that electromagnetic interaction is associated with a particularly intense force if compared with gravitational interaction: the electric force between an electron and a proton in a hydrogen atom is 1039 times higher than the gravitational force between the two.

To facilitate the generation of electrostatic charges is usually used an electrostatic generator; among the most famous are the perpetual electrophorus and the Van de Graaff generator. The practical exploitation of the force exerted between the electric charges happens for example with the ionic thruster and the electrostatic ionic thruster, while the natural or induced manifestation of this electric force is visible with the corona effect or the dispersing power of the spikes (among which the St. Elmo’s fire).

The first investigations on this force are had in Greece in 600 B.C. with Thales of Miletus and Theophrastus, and concern electrostatic experiments with amber and silk (or alternatively wool). Subsequently, more in-depth studies took place from the sixteenth to the nineteenth century: in particular, until the middle of the eighteenth century were known only the qualitative aspects of the electrical force: then began to study also its quantitative properties, so that the idea of a similarity with the force of gravity. Aspects such as:

  • the presence of a universal constant independent from the adopted system of measure;
  • the direct proportionality with the first power of the interacting point particles;
  • the inverse proportionality with the square of the distance.

Between 1777 and 1785 was Charles Augustin de Coulomb to prove experimentally that indeed the electric force was proportional to the inverse of the square of the distance; but he was not the first, since the same experiments of Coulomb were previously conducted by the English Henry Cavendish, who for his bizarre personality did not publish most of his work. This was the first attempt to understand the workings of the electric force.

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